That's a Sejin SPR-8630. From Korea.
It has a better key size than the Cherry 4100 so a touch typist can slip straight over to it. It is actually about my favorite ever membrane.
Sejin were some of the first keyboards we ever sold, they had a left handed back then, and these. They sell really well into the ergo market where people are looking to get the mouse as close in as they can.
There are a lot of cheapies in the same format now but this one and the Cherry are the only ones I like.